Organophosphorus Nerve Agents: Types, Toxicity, and Treatments

Mukherjee, Sudisha; Gupta, Rinkoo Devi

doi:https://doi.org/10.1155/2020/3007984

Journal of Toxicology

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Abstract Introduction Conclusions Abbreviations Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Review Article | Open Access

Volume 2020 | Article ID 3007984 | https://doi.org/10.1155/2020/3007984

Organophosphorus Nerve Agents: Types, Toxicity, and Treatments

Sudisha Mukherjee¹and Rinkoo Devi Gupta¹

Academic Editor: Orish Ebere Orisakwe

Received10 Feb 2020

Revised30 Aug 2020

Accepted10 Sept 2020

Published22 Sept 2020

Abstract

Organophosphorus compounds are extensively used worldwide as pesticides which cause great hazards to human health. Nerve agents, a subcategory of the organophosphorus compounds, have been produced and used during wars, and they have also been used in terrorist activities. These compounds possess physiological threats by interacting and inhibiting acetylcholinesterase enzyme which leads to the cholinergic crisis. After a general introduction, this review elucidates the mechanisms underlying cholinergic and noncholinergic effects of organophosphorus compounds. The conceivable treatment strategies for organophosphate poisoning are different types of bioscavengers which include stoichiometric, catalytic, and pseudocatalytic. The current research on the promising treatments specifically the catalytic bioscavengers including several wild-type organophosphate hydrolases such as paraoxonase and phosphotriesterase, phosphotriesterase-like lactonase, methyl parathion hydrolase, organophosphate acid anhydrolase, diisopropyl fluorophosphatase, human triphosphate nucleotidohydrolase, and senescence marker protein has been widely discussed. Organophosphorus compounds are reported to be the nonphysiological substrate for many mammalian organophosphate hydrolysing enzymes; therefore, the efficiency of these enzymes toward these compounds is inadequate. Hence, studies have been conducted to create mutants with an enhanced rate of hydrolysis and high specificity. Several mutants have been created by applying directed molecular evolution and/or targeted mutagenesis, and catalytic efficiency has been characterized. Generally, organophosphorus compounds are chiral in nature. The development of mutant enzymes for providing superior stereoselective degradation of toxic organophosphorus compounds has also been widely accounted for in this review. Existing enzymes have shown limited efficiency; hence, more effective treatment strategies have also been critically analyzed.

1. Introduction

The usage of pesticides for suicidal poisoning resulted in ∼110,000 deaths each year during the span of 2010 to 2014, comprising 13.7% of total global suicides [1]. In India, the toxicity of these pesticides came into prominence around the year 1962 [2], which is estimated to be ∼168,000 deaths annually, that is, 19.7% of global suicides [1]. Extensive exposure to organophosphorus pesticides leads to various complications such as acute myocardial injury [3], cognitive impairment [4], and neuropsychiatric disorders in farmers [5]. Some organophosphorus pesticides also bioaccumulate in the environment [6], cause harm to birds such as vultures [7], and severely affect aquatic lifeforms [8] such as Senegalese sole and Solea senegalensis [9]. In Iran, Japan, and other terrorist attacks [10] including the assassination of Kim Jong-nam in Malaysia [11], these compounds were used as warfare agents, due to which, many international protocol and treaties have been entrenched. The Organisation for the Prohibition of Chemical Weapons (OPCW) was formed for implementing the Chemical Weapons Convention, which came in force on 29 April 1997. This body with its 193 member states supervises the global venture to permanently or verifiably eliminate chemical weapons [12].

2. Types of Organophosphorus Compounds

Organophosphorus compounds (OPCs) are organic chemicals derived from phosphoric acids and its derivatives and contain at least one carbon-phosphorus bond. The pentavalent types of phosphorus-containing compounds are primarily used in industrial and environmental applications. The substituents attached to the phosphorus of these esters of phosphoric acids play a vital role in toxicity [13]. Organophosphorus pesticides are thiols, amides, or esters of phosphonic, phosphinic, phosphoric, or thiophosphoric acids with two additional organic side chains of the phenoxy, cyanide, or thiocyanate group [14]. Some of the OPCs belong to the phosphonothioates (S-substituted), and phosphonofluoridate categories comprise of nerve agents, commonly known as chemical warfare agents [15].

These nerve agents can be classified into four types: (1) the G-series agents which were developed by Germans and include tabun (GA), sarin (GB), soman (GD), and cyclosarin (GF) (Figures 1(a)–1(d)). (2) V-series agents, where V stands for venomous, include VE, VG, VM, and VX [11], and Chinese VX and Russian VX [16] (Figure 1(e)). (3) GV-series which have the combined properties of both series G and V, for example, GV, 2-dimethylaminoethyl-(dimethylamido)-fluorophosphate [17]. Generally, the G-series agents are less toxic compared to the V series [18]; (4) Novichok series of compounds, for example, substance-33, A230, A232, A234, Novichok-5, and Novichok-7 [19, 20]. Dr. Mirzayanov was first person to detail the development of the first three compounds, namely, substance-33, A230, and A232 at the GosNIIOKhT facility, Russia [21]. These compounds were unitary agents. Later, in the year 1989, the first Binary agent known as Novichok-5 was synthesised with Unitary A232 as its base structure [21]. Novichok agents are liquid in form, although they can convert into dusty formulation by the adsorption of liquid droplets on carriers such as silica gel, pumice, fuller’s earth, or talc [22]. Hydrolysis of A230, A232, and A234 was seen to be slower in comparison to G- and V-series agents [23]. Generally owing to the secrecy surrounding their research, there is a huge debate regarding the structures of these compounds, and so, many different versions of structures have been speculated (Figures 1(f)–1(n)).

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The fluoride-releasing volatile soman and sarin, cyanide-releasing tabun, and the thiocholine-releasing VX have a stereogenic phosphorus atom. All of these OPCs have two enantiomers P(−) and P(+), except for Soman which has two chiral atoms, one being a carbon centre and other being the phosphorus, which has four enantiomeric forms: C (+)P(+), C (+)P(−), C (−)P(+), and C (−)P(−) [24]. Comprehensive structural information regarding different types and isomers of the OPC nerve agents has been recently compiled and thoroughly reviewed [13, 15, 25, 26]. Stereoisomers play a crucial role in the context of the range of toxicity of the compound. Generally, P(−) enantiomers are more toxic in nature [27].

3. Physiological Effects

OPCs cross the respiratory epithelial and dermal membrane easily and gets distributed, especially in fat tissues. In suicidal cases, the absorptions through gastric mucosa have been reported. Most of these OPCs are inactive in their native form which converts to their active forms by a biotransformation process. This biotransformation process happens through oxidation of different groups such as sulphur group (e.g., parathion and malathion), thioether (e.g., disulfoton), amides (e.g., schradan and dichrotophos), and hydroxylation of the alkyl group (e.g., triorthocresylphosphate). Some OPCs may also undergo nonoxidative alteration to form toxic compounds as in the case of insecticides Trichlorfon and Nale [28]. After, the biotransformation, these OPCs can interact and inhibit the AChE which leads to the cholinergic crisis. In addition, it also interacts with certain biomolecules other than the AChE. Hence, the toxicity of OPCs has been divided into two categories, i.e., cholinergic and noncholinergic effects which have been discussed below in detail.

3.1. Cholinergic Effect

Acetylcholine (ACh) is a neurotransmitter [29] and interacts with the muscarinic acetylcholine receptors (mAChRs) which use G-protein signalling pathways [30]. This interaction has shown to play a vital role in the regulation of heart rate, contraction of smooth muscles, secretion of glands, and other CNS fundamental functions [30, 31]. ACh also interacts with nicotinic acetylcholine receptors (nAChRs) [30] (Figure 2) which have 5 subunits [32]. nAChRs uses ligand-gated channel [30, 33, 34] and contributes to cognitive process [33, 35]. After a normal transmission of the neural signalling, the ACh binds with AChE [30, 36, 37] and gets degraded to acetate and choline (Figure 2). Each AChE molecule degrades about 25,000 molecules of ACh per second [38]. The ACh sits on lipophilic, uncharged anionic site of AChE with an electrostatic interaction [39, 40]. In this process, the amino acid Trp84 plays a vital role [41]. However, this set-up is inhibited reversibly and irreversibly by OPCs. The OPCs bind with AChE to form a complex (OPC, enzyme complex) which hinders the ACh hydrolysis, causing excessive cholinergic effect and rapid death within minutes. The intermediate syndrome has been reported to occur before 24 hours after exposure as well as, after 96 hours after exposure of OPCs [42]. This syndrome has been speculated to be related to the myopathy accompanied by weakness in respiratory muscles [43]. During respiratory complications, alveolar fluid, bronchorrhea acute respiratory disorder, aspiration pneumonitis, and pneumonia have also been reported [44].

Figure 2

Depiction of cellular interaction of AChE, Ach, and OPCs. (a) Choline released from ACh hydrolysis, moves to axon where it reacts with acetyl moiety of co-acetyl to from ACh by an enzyme ChAT (choline acetyltransferase) and gets stored in vesicles along with cotransmitters such as ATP. (b) The influx of calcium results in the fusion of membranes. (c) Fusion leads to release of ACh into neuron junctions. (d) Interaction of ACh with nAChRs and mAChRs. (e) Signalling to different physiological targets. (f) Excess ACh after signalling, interacts with AChE and degrades into choline and acetate. (g) OPC binds with AChE and leads to increased ACh and endless signalling.

Sometimes removal of a functional group from the OPCs such as nerve agents results in a stronger and permanent bond between the nerve agent and enzyme resulting in an irreversible inactivated state of enzyme, and this scenario is called ageing of the enzyme. The pace of enzyme ageing greatly varies with different nerve agents [45]. The serine residue of the catalytic site of cholinesterase [46] plays a vital role in ageing. Theoretically, it has been seen that Novichok also binds with acetylcholinesterase (AChE, E.C. 3.1.1.7) and leads to ageing of the enzyme [20, 47]. The stereochemistry of nerve agents also determines the extent of reactivation of the AChE [11]. Organophosphorus pesticides are also potent inhibitors of neuropathy target esterase (NTE). It has been reported in rats that dichlorvos decreases the Km value of NTE and, therefore, reduces the affinity of the enzyme for its substrate phenyl valerate [48].

3.2. Noncholinergic Effects

Some OPCs also cause another neurotoxicity known as organophosphate-induced delayed polyneuropathy (OPIDP) [49]. These toxicities result in the tingling effect of hands and feet, subsequently sensory loss, muscular weakness, and flaccidity of distal skeletal muscles, and ataxia [50, 51], after 2-3 weeks of exposures. OPIDP is also categorized as distal sensorimotor axonopathy [52] due to the inhibition of NTE [53]. NTE consists of both phospholipase and esterase activities [54], and belongs to patatin-like phospholipase domain-containing proteins (PNPLAs1-9) [55]. Mutations in NTE (PNPLA6) has been linked with the CNS and PNS alteration leading to congenital disorders [56]. OPIDP to occur about 70% of NTE inhibition has been seen to be necessary in the chicken [57]. Apart from inhibiting esterase, OPCs such as dichlorvos also showed inhibition of acyl peptide hydrolase which is a peptidase in a rat model [58]. The Inhibition of encephalin metabolism [59], endocannabinoid metabolism system [60, 61], and many lipases by OPCs [62] have also been reported. In addition, these compounds are also associated with oxidative stress which has been reported in many in vivo, in vitro, and human studies [63, 64].

4. Treatment Strategies for Organophosphorus Poisoning

Although different antidotes are employed to treat the nerve agent poisoning, yet proficient recovery of aged AChE has been a challenge. Intravenously or intramuscularly introduced bioscavengers interact with OPCs and lead to neutralization reaction within bloodstream [65]. These can also be incorporated into the skin as active topical skin protectant [66] or have also shown neutralization effect to prevent OPC poisoning in macaques when introduced as aerosols or intravenously [67, 68]. Generally, bioscavengers can be divided into three types: (1) stoichiometric enzymes which bind with the OPCs and result in inactivation; (2) catalytic bioscavenger which hydrolyses the OPCs and degrades them to nontoxic components; and (3) pseudocatalytic bioscavengers which are a mixture of stoichiometric bioscavengers with a chemical reactivator such as oxime [69] (Figure 3).

There are many reactivators which are used to reactivate an AChE-OPC complex such as pralidoxime (PAM-2), trimedoxime (TMB-4), obidoxime (LuH-6, toxogonin) [10], and HI-6 (asomine, 1-(2′-hydroxyiminomethy-1′ pyridinum)- 3-(4′-carbomonyl-1-pyridinium)) [11]. For an enzyme to become a potential bioscavenger, it must overcome a number of impediments. It should have a high bimolecular rate and a large spectrum of activity with more enantiomeric preferences toward the toxic isomers. It should have long mean residence time in the body. It should not have an iatrogenic effect or/and any contaminants in it. It should also be easily available from natural sources, thermostable and economically affordable [70]. Naturally occurring enzymes which have organophosphatase activity as one of their promiscuous nature have been used as bioscavengers. These enzymes provide a prophylactic effect and neutralize the OPCs before they reach their target (Figure 4) in the blood [26]. Hence, different types of catalytic bioscavengers have been discussed below in detail.

4.1. Catalytic Bioscavengers

The stoichiometric bioscavengers are single-use enzymes with no turnover as one molecule of it binds with a single OPC for neutralization. Hence, the cost/dose of these enzymes is high compared to which the catalytic bioscavengers are multiple-time enzymes showing turnover and thus have low dose and high efficiency [26, 70]. However, unlike stoichiometric bioscavengers, some catalytic bioscavengers exhibit stereospecificity which limits the complete degradation of OPCs. Catalytic bioscavenger can be categorized as (1) bacterial type which includes enzymes such as methylparathion hydrolase, organophosphate hydrolase, and phosphotriesterase, and (2) mammalian type which includes enzymes such as human senescence marker protein 30, paraoxonase, and human triphosphate nucleotidohydrolase. Furthermore, the catalytic efficiencies, specificity, and mechanism of some of these catalytic bioscavengers are being discussed here.

4.1.1. Bacterial Catalytic Bioscavenger

(1) Phosphotriesterase (PTE). Phosphotriesterase (PTE) was first isolated from soil bacterium Flavobacterium sp. and Pseudomonas diminuta [71]. This protein belongs to the amidohydrolase superfamily and is a homodimeric metalloprotein with a TIM barrel structure (α/β) 8 folds [72], and each of its monomers consists of two zinc metal ions. Among the zinc metal ions, the one buried deeper in the structure is the α metal and coordinates with Asp301, His55, and His57, whereas the other known as the β metal is exposed to solvent and coordinates with His201 and His230. The zinc ions are bridged by a water molecule and Lys169 residue [73]. The residues associated with a small pocket are Gly60, Leu303, Ser308, and Ile106, while the large pocket is defined by His257, His254, Met317, and Leu271. Phe306, Phe132, Trp131, and Tyr309 are the residues in the hydrophobic leaving pocket [72]. A mutant (His257Tyr/Leu303Thr) of bacterial PTE showed catalytic efficiency approximately 10 times more than wild type for sarin and cyclosarin, and of about 100 times more for soman. It also showed stereospecificity and enhanced activity toward the P(−) enantiomer of cyclosarin [74, 75].

(2) Phosphotriesterase-Like Lactonase (PLL). PLL, the closest structural homologues to PdPTE, belongs to the amidohydrolase protein family. It catalyses lactones such as acyl-homoserine lactones (AHLs) by hydrolytic cleavage of their intracellular ester bond, and shows phosphotriesterase activity for OPCs. This enzyme also has (β/α) 8-barrel fold structure with a divalent metallic centre, which governs the catalytic activity [76]. PLL has been isolated from aerobic bacteria such as Pseudomonas pseudoalcaligenes [77] and extremophiles such as hyperthermophilic bacteria [78, 79], and from archaea [80]. PLL from Deinococcus radiodurans (drPLL) is thermostable, robust, and soluble in nature. Random mutagenesis, rational protein designing, and crucial screening have been applied to create variants of PLL with enhanced organophosphatase activity. Among all the mutants, drPLL 10 (Tyr28Leu/Asp71Asn/Tyr97Phe/Glu101Gly/Glu179Asp/Val235Leu/Pro274Leu) showed about 2800-fold decrease in lactonase activity with δ-lactone and an increase in OPCs hydrolysis up to 6.9 × 10⁴ fold [76]. Likewise, another thermostable lactonase from Geobacillus kaustophilus HTA426 (GkaP) after site-specific mutagenesis showed increased OPC catalysis. The mutant GkaP (Phe28Ile/Tyr99Leu/Thr171Ser/Phe228Leu/Asn269Ser/Val270Gly/Trp271Cys/Gal273Asp) showed an increase in catalytic efficiency by approximately 230 folds [79]. Another PLL SsoPox isolated from Sulfolobus solfataricus has shown a promising OPC degrading capacity [25].

(3) Methyl Parathion Hydrolase (MPH). Bacterial methyl parathion hydrolase (MPH, EC 3.1.8.1) was first identified in Plesiomonas sp. strain M6, which uses methyl parathion as its sole C and N sources [25, 81]. It consists of a dimeric structure with each subunit having mixed hybrid binuclear zinc. The ions are coordinated with His147, His149, His152, Asp151, His302, and His234 residues, and a water molecule. Asp255 and water molecule make a bridge between the zinc ions. The catalytic centre contains Phe196, Trp179, and Phe119 at the entrance [82]. Various recombinant MPHs have shown to be highly active on hydrolysing methyl parathion and other OPCs such as dichlorvos or malathion [83]. OPHC2 similar to MPH has been isolated and identified from Pseudomonas pseudoalcaligenes strain C2-1 [84] and Stenotrophomonas strain SMSP-1 [85]. Random mutation with MPH from P. stutzeri resulted in a 5-fold increase in chlorpyrifos hydrolysis, whereas the variant PoOPHm2 showed 6962- and 106-fold increases for methylparathion and ethyl paraoxon [86, 87], respectively.

(4) Organophosphate Acid Anhydrolase (OPAA). OPAA (EC. 3.1.8.2) from Alteromonas sp. [73, 88] with phosphotriesterase and prolidase activity is a tetramer that is a dimer of a dimer structure [89, 90] and the functional oligomeric state of the enzyme. Each of the dimer subunits consists of a C-terminal with pita bread fold and N-terminal globular domain. The C-terminal consists of binuclear Mn²⁺ at the cleft. The solvent-exposed metal is ligated with His336 and Glu381, whereas the other metal is ligated in divalent orientation to Asp244, and these two metals are bridged by two other carboxylate ligands, Glu420 and Asp255. OPAA has prolidase activity specific to dipeptides with the second residue as Proline [73]. Its binding site comprises of three pockets: small, large, and leaving. The small pocket is lined with Try212, Val342, and His343, and capped with Asp45′ at N-terminal domain of the opposite subunit of dimer. The large pocket is associated with Leu225, His226, His332, and Arg418, and capped with Trp89′ from another subunit, and the leaving pocket consists of Tyr292 and Leu366 [73, 74, 91]. The proposed mechanism for OPAA enzymes states the presence of hydroxide bridge between two manganese (II) ions which start the nucleophilic attack on the phosphorus centre leading to the formation of an intermediate compound which then departs with the leaving group. His343 forms H-bonds with free phosphoryl oxygen and assists the positioning of the substrate [25, 73, 74].

(5) Diisopropyl Fluorophosphatase (DFPase). Diisopropyl fluorophosphatase (DFPase, EC 3.1.8.2) from Loligo vulgaris squid is a phosphotriesterase that hydrolyses various OPCs [92]. It is a 35 kDa protein with a six-bladed β propeller structure [93, 94]. It has two calcium ions: one is responsible for structural integrity, and the other is responsible for the catalytic reactions. Asp229 is crucial for the activity of this enzyme, whereas the Glu21 is needed for calcium binding [95]. It hydrolyses P-F bond in the OPCs such as DFP molecule and releases the fluoride and diisopropylphosphate which is nontoxic. In this process, the fluorophosphate compound gets polarized by calcium ion stimulating attack by the carboxylate group and results in the fluoride release [93, 94, 96, 97].

4.1.2. Mammalian Catalytic Bioscavenger

(1) Paraoxonase (PON). The paraoxonase (E.C. 3.1.8.1.) family of proteins has three genes, PON1, PON2, and PON3, located on chromosome 7 in human (7q21.3-22.1), and chromosome 6 in the mouse. There is a 60% similarity in amino acid, and 70% in the nucleotide sequence within this family. PON1 with 355 amino acid weighs 43–47 kDa and has a cylindrical β-propeller feature with β strands linked by a disulphide bridge [98–100]. Two calcium ions are present at the centre, of the protein, one of which helps in catalytic activity, and the other maintains the structural stability of the enzyme [101, 102]. An apoprotein A-I stabilizes the association with HDL and enhances lactonase activity [98, 103]. When associated with HDL, it helps in lowering the oxidation of LDL [98, 103, 104]. It is mainly synthesised in the liver and secreted to plasma, but it is also present in the brain, small intestine, and kidney [98, 99, 105]. PON2 is associated with an inflammatory reaction, antioxidant property, and plays a role in defending against atherosclerosis. It is found intracellularly in tissues such as the lungs, placenta, testes, and heart, and mainly in the liver [98, 106, 107], whereas PON3 is found in the kidney and liver and displays antioxidant and antiatherosclerotic effect [98, 108]. PON proteins are related to various hydrolytic activities, namely, lactonase activity, arylesterase activity, and organophosphatase activity. Among all the PON proteins, PON1 exhibits all the three activities, whereas PON2 is linked with only lactonase activity, and PON3 shows lactonase and arylesterase activities [98, 104, 109].

PON1 gene is highly polymorphic with 184 SNPs, which includes 8 in the promoter region and 174 in the gene sequence [110, 111]. PON1 192 Gln/Arg and 55 Met/Leu polymorphisms have been associated with many health risk factors. It has been reported that homozygous 55 Leu/Leu shows lower LDL than heterozygous 55 Leu/Met, while 192Arg/Arg shows lower HDL and higher LDL compared to 192Gln/Gln [98]. Homozygous 192Arg/Arg and 55Met/Met are associated with high levels of thiobarbituric acid-reactive substances, conjugated dienes, and low level of GSH in blood, whereas the homozygous counterparts, i.e., 192Gln/Gln and 55Leu/Leu, showed completely opposite effect, testifying that 192Gln/Gln and 55Leu/Leu have a protective role against oxidative stress [112]. Some other polymorphisms such as PON2 148Ala/Gly and PON3 311Cys/Ser, and polymorphisms in the promoter region such as 107Cys/Thr, 162Ala/Gly, and 907Gly/Cys [110] of PON1 have been studied for their relationship with heart diseases. Homozygous PON1 107Cys/Cys has been reported to be associated with high HDL [98, 113].

(2) Senescence Marker Protein 30 (SMP30). Human senescence marker protein 30 (HuSMP30; EC 3.1.1.17) is a 34 kDa protein [114] with a six bladed β-propeller structure which consists of a single metal ion binding centre. It is primarily expressed in the liver and kidney tissues. It is found in the lungs, kidney, liver, testes, and cerebrum, and is conserved in the vertebrates [115]. In humans, it is located at p11.3-q11.2 of the X chromosome [114]. Like PON1, it has also been reported to show lactonase [116] activity as its physiological function; however, it also catalyses the hydrolysis of an OPC, diisopropyl fluorophosphate, thus acting as DFPase [117]. SMP30 is also referred to as regucalcin due to its high affinity with calcium indicating its role in maintaining calcium homeostasis in the cells [118–120]. The penultimate step of ascorbic acid biosynthesis in nonprimates is catalysed by SMP30 [121]; however, the ascorbic acid biosynthesis pathway is not functional in human. These analyses suggest that SMP30 might play an important role in calcium homeostasis and providing protection against OPC poisoning in human. A recent study from our research group demonstrated that both mouse and human SMP30 showed organophosphate hydrolase activity in the presence of Ca²⁺ and Zn²⁺, thus displaying metal-dependent promiscuous activity [116]. A recombinant HuSMP30 has also been expressed with chaperones as a soluble protein and has been characterized for its DFPase activity [122].

(3) Human Triphosphate Nucleotidohydrolase (dUTPase). Human triphosphate nucleotidohydrolase (dUTPase; EC: 3.6.1.23) is a trimerically structured enzyme with a 3-fold axis. The subunits of this protein interact through twisted β-sheets thus resulting in burying the hydrophobic surfaces about the axis [123]. It converts deoxyuridine triphosphate to deoxyuridine monophosphate [124] and prevents DNA uracilation, and maintains genome integrity [125]. It consists of three active sites and requires divalent Mg²⁺ for its activity. It is a potent enzyme and has shown to have a stereoselective preference toward P(−) enantiomer of VX [126]. Table 1 contains the list of variants of these organophosphatase and their compared activity with their respective wild types.

4.2. Stereoselective Degradation

Enzymes have the ability to differentiate between the enantiomers of the substrate, and this ability is termed as the stereospecificity of an enzyme. This is a vital property of a biocatalyst; it allows the biocatalyst to undergo either fast or slow reaction on the basis of the reaction orientation. This property is exploited in chemical, pharmaceutical, and agrochemical industries [141]. Since the naturally occurring enzymes have inefficient stereoselectivity/regioselectivity and thermostability, they have not been able to achieve eminence in practical procedures. The emergence of protein engineering techniques such as direct evolution has proven to be a vital tool in engendering various genetic amendments to construct variants of natural enzymes with superior activity compared to their wild types [128, 140–143].

A special substrate asymmetrical fluorogenic organophosphate, CMP-MeCyC, was created and used to study the stereoselective hydrolysis by mammalian wild-type PON1 and its variants, in which a variant 4.27/V346A (Leu69Val/Ser138Leu/Ser193Pro/Asn287Asp/Val346Ala) showed the highest detoxification. The wild type of PON1 displayed a preference for the P (+) isomer, whereas the mutated variant of PON1 showed more active hydrolysis toward P(−) isomers of CMP-MeCyC [144]. In another experiment, mutant with H115W mutation exhibited 270–380-fold increase in hydrolytic activity for parathiol, whereas mutant with Leu69Val results in 10–100-fold increase in activity for DFP, cyclosarin, and soman. PON1 variants with Val346Ala, Leu69Val/Ser193Pro/Val346Ala, and Leu69Val/Ser138Leu/Ser193Pro/Asn287Asp/Val346Ala have resulted in 4- to 10-fold increase in the hydrolysis of ChPo and P-F containing organophosphorus esters [145]. Another variant 4E9 (Leu69Gal, Ser111Thr, His115Trp, His134Arg, Phe222Ser, Thr332Ser) has shown to be an active variant in hydrolysing P(−)-CMP-coumarin and P(−)-CMP-F [130] (Figures 5(a) and 5(b)).

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Figure 5

Illustration represents residues important for stereoselectivity of the enzymes: (a) PON1 cartoon structure with different coloured sphere-shaped residues; (b) PON1 residues as sticks; (c) PTE cartoon structure with different coloured sphere-shaped residues; (d) PTE residues as sticks; (e) OPAA cartoon structure with different coloured sphere-shaped residues; (f) OPAA residues as sticks. (For creating the above structures, basic structures were taken from PDB ID: 1V04, 3CAK, and 3L7G, and PyMOL software was used.)

The large, small, and leaving pockets of enzyme PTE play a crucial role in the stereoselectivity of the enzyme and are manipulated by the mutation process to enhance, reverse, and relax this stereoselectivity. Decreasing the large pocket and enlarging the small pocket by the rational engineering of PTE invert the enantiomer selectivity of the wild type. The wild type prefers the hydrolysis of the less-toxic P (+) enantiomer of GB, GD, and GF, and their analogous, whereas the mutants GWT, GGY, and YT displayed preference toward P(−) enantiomer hydrolysis. The molecular dynamics simulation also revealed that the leaving group orientation plays an important factor for chiral selectivity. Mutant with mutation His254Gal/His257Trp/Leu303Thr showed a preference toward the P(−) enantiomers of sarin [72, 138]. Another mutant Ile106Ala/Phe132Ala/His257Tyr has also shown a high preference toward the P(−) enantiomer of sarin [72]. Mutant C74 with mutations His254Asn and Ile106Ala showed a reduction in P(+) isomer preference and increase in P(−) isomer preference for RVX [146] (Figures 5(c) and 5(d)). Similarly, OPAA mutant FLYD (Try212Phe/Val342Leu/Ile215Try/His343Asp) with four mutations showed 16-fold increase in catalysis compared to wild type, and broader stereospecificity for VR [74] (Figures 5(e) and 5(f)).

5. Conclusions and Future Perspectives

The indirect or direct exposures of various OPCs, especially the nerve agents, have proven to be an utmost important threat causing severe health issues. The quantity and the route of OPC exposure may lead to acute, intermediate, or delayed symptoms in humans. Although these chemicals are generally used extensively as pesticides and antiacetylcholinesterase for treatment purpose in diseases such as Alzheimer’s, their long-term side effect proves to be a major concern. Majority of these chemicals are chiral compounds and are generally present in their different enantiomeric forms. Existing antidotes have limited efficiency due to which research for more effective treatment strategies is being carried out globally. This has led to manipulate the promiscuous nature of catalytic bioscavengers such as paraoxonase and PTE via protein engineering techniques to generate mutants with enhanced ability to degrade the OPCs before they reach their target niches. Techniques such as directed molecular evolution where different types of mutations are employed to generate mutants which have higher efficiency toward more toxic P(−) isomers, are thermostable and are able to hydrolyse a racemic mixture of OPCs effectively. These superior mutants with better delivery systems are potential OPC-hydrolysing agents in the near future.

Abbreviations

OPCW:	Organisation for the Prohibition of Chemical Weapons
OPCs:	Organophosphorus compounds
ACh:	Acetylcholine
AChE:	Acetylcholinesterase
mAChRs:	Muscarinic acetylcholine receptors
nAChRs:	Nicotinic acetylcholine receptors
PON:	Paraoxonase
PTE:	Phosphotriesterase
OPAA:	Organophosphate acid anhydrolase
OPIDN:	Organophosphate-induced delayed neuropathy
NTE:	Neuropathy target esterase
MPH:	Methylparathion hydrolase
PLL:	Phosphotriesterase-like lactonase
SMP30:	Senescence marker protein 30
AHL:	Acyl-homoserine lactone
ChAT:	Choline acetyl transferase
PNPLAs:	Patatin-like phospholipase domain-containing proteins
dUTPase:	Human triphosphate nucleotidohydrolase.

Data Availability

All the relevant data used to support the findings of this study are included in the article.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

RDG thanks DRDO (LSRB-297/BTB/2017) and SERB (EMR/2016/007246) for financial supports. SM thanks DRDO (LSRB-297/BTB/2017) for getting Junior Research Fellowship.

References

E. J. Mew, P. Padmanathan, F. Konradsen et al., “The global burden of fatal self-poisoning with pesticides 2006–15: systematic review,” Journal of Affective Disorders, vol. 219, pp. 93–104, 2017.
View at: Publisher Site | Google Scholar
P. K. Sinha and A. Sharma, “Organophosphate poisoning : a review,” Medical Journal of Indonesia, vol. 12, no. 2, p. 120, 2003.
View at: Publisher Site | Google Scholar
K.-X. Chen, X.-H. Zhou, C.-A. Sun, and P.-X. Yan, “Manifestations of and risk factors for acute myocardial injury after acute organophosphorus pesticide poisoning,” Medicine (Baltimore), vol. 98, no. 6, Article ID e14371, 2019.
View at: Publisher Site | Google Scholar
L. Pang, J. Liu, W. Li, Y. Xia, and J. Xing, “Serum ubiquitin C‐terminal hydrolase L1 predicts cognitive impairment in patients with acute organophosphorus pesticide poisoning,” Journal of Clinical Laboratory Analysis, vol. 33, no. 7, Article ID e22947, 2019.
View at: Google Scholar
A. Serrano-Medina, A. Ugalde-Lizárraga, M. Bojorquez-Cuevas et al., “Neuropsychiatric disorders in farmers associated with organophosphorus pesticide exposure in a rural village of northwest México,” International Journal of Environmental Research and Public Health, vol. 16, no. 5, p. 689, 2019.
View at: Publisher Site | Google Scholar
B. M. Mercado-Borrayo, S. Cram Heydrich, I. Rosas Pérez, M. Hernández Quiroz, and C. Ponce De León Hill, “Organophosphorus and organochlorine pesticides bioaccumulation by Eichhornia crassipes in irrigation canals in an urban agricultural system,” International Journal of Phytoremediation, vol. 17, no. 7, pp. 701–708, 2015.
View at: Publisher Site | Google Scholar
P. I. Plaza, E. Martínez-López, and S. A. Lambertucci, “The perfect threat: pesticides and vultures,” Science of The Total Environment, vol. 687, pp. 1207–1218, 2019.
View at: Publisher Site | Google Scholar
R. J. R. Mamta, R. J. Rao, and K. A. Wani, “Status of organochlorine and organophosphorus pesticides in wetlands and its impact on aquatic organisms,” Environmental Claims Journal, vol. 31, no. 1, pp. 44–78, 2019.
View at: Publisher Site | Google Scholar
J. B. Ortiz-Delgado, V. Funes, and C. Sarasquete, “The organophosphate pesticide -OP- malathion inducing thyroidal disruptions and failures in the metamorphosis of the Senegalese sole, Solea senegalensis,” BMC Veterinary Research, vol. 15, no. 1, p. 57, 2019.
View at: Publisher Site | Google Scholar
M. Balali-Mood and H. Saber, “Recent advances in the treatment of organophosphorous poisonings,” Iranian Journal of Medical Sciences, vol. 37, no. 2, pp. 74–91, 2012.
View at: Google Scholar
S. M. Bester, M. A. Guelta, J. Cheung et al., “Structural insights of stereospecific inhibition of human acetylcholinesterase by VX and subsequent reactivation by HI-6,” Chemical Research in Toxicology, vol. 31, no. 12, pp. 1405–1417, 2018.
View at: Publisher Site | Google Scholar
“Organisation for the prohibition of chemical weapons,” 2019, https://www.opcw.org/.
View at: Google Scholar
B. Balali-Mood, “Chemistry and classification of OP compounds,” in Basic and Clinical Toxicology of Organophosphorus Compounds, pp. 1–23, Springer, London, UK, 2014.
View at: Google Scholar
S. Kumar, G. Kaushik, and J. F. Villarreal-Chiu, “Scenario of organophosphate pollution and toxicity in India: a review,” Environmental Science and Pollution Research, vol. 23, no. 10, pp. 9480–9491, 2016.
View at: Publisher Site | Google Scholar
R. C. Gupta, “Classification and uses of organophosphates and carbamates,” in Toxicology of Organophosphate & Carbamate Compounds, pp. 5–24, Elsevier, Amsterdam, Netherlands, 2006.
View at: Google Scholar
A. Kranawetvogl, J. Küppers, M. Siegert et al., “Bioanalytical verification of V-type nerve agent exposure: simultaneous detection of phosphonylated tyrosines and cysteine-containing disulfide-adducts derived from human albumin,” Analytical and Bioanalytical Chemistry, vol. 410, no. 5, pp. 1463–1474, 2018.
View at: Publisher Site | Google Scholar
M. Moshiri, E. Darchini-Maragheh, and M. Balali-Mood, “Advances in toxicology and medical treatment of chemical warfare nerve agents,” Daru, vol. 20, no. 1, p. 81, 2012.
View at: Publisher Site | Google Scholar
J. Bajgar, Nerve Agents Poisoning and its Treatment in Schematic Figures and Tables, Elsevier, Amsterdam, Netherlands, 2012.
P. R. Chai, B. D. Hayes, T. B. Erickson, and E. W. Boyer, “Novichok agents: a historical, current, and toxicological perspective,” Toxicology Communications, vol. 2, no. 1, pp. 45–48, 2018.
View at: Publisher Site | Google Scholar
T. C. C. Franca, D. A. S. Kitagawa, S. F. d. A. Cavalcante, J. A. V. da Silva, E. Nepovimova, and K. Kuca, “Novichoks: the dangerous fourth generation of chemical weapons,” International Journal of Molecular Sciences, vol. 20, no. 5, pp. 1–10, 2019.
View at: Publisher Site | Google Scholar
A. E. Smithson, V. S. Mirrzayanov, and R. Lajoie, Chemical Weapons Disarmament in Russia: Problems and Prospects, The Stimson Center, Washington, DC, USA, 1995.
D. H. Ellison, Handbook of Chemical and Biological Warfare Agents, vol. 2, Taylor and Francis Group, Boca Raton, FL, USA, 2008.
S. P. Harvey, L. R. McMahon, and F. J. Berg, “Hydrolysis and enzymatic degradation of Novichok nerve agents,” Heliyon, vol. 6, no. 1, 2020.
View at: Publisher Site | Google Scholar
H. P. Benschop and L. P. A. De Jong, “Nerve agent stereoisomers: analysis, isolation and toxicology,” Accounts of Chemical Research, vol. 21, no. 10, pp. 368–374, 1988.
View at: Publisher Site | Google Scholar
P. Jacquet, D. Daudé, J. Bzdrenga, P. Masson, M. Elias, and E. Chabrière, “Current and emerging strategies for organophosphate decontamination: special focus on hyperstable enzymes,” Environmental Science and Pollution Research, vol. 23, no. 9, pp. 8200–8218, 2016.
View at: Publisher Site | Google Scholar
S. Costanzi, J.-H. Machado, and M. Mitchell, “Nerve agents: what they are, how they work, how to counter them,” ACS Chemical Neuroscience, vol. 9, no. 5, pp. 873–885, 2018.
View at: Publisher Site | Google Scholar
M. Mousavi, E. Hellström-Lindahl, Z.-Z. Guan, I. Bednar, and A. Nordberg, “Expression of nicotinic acetylcholine receptors in human and rat adrenal medulla,” Life Sciences, vol. 70, no. 5, pp. 577–590, 2001.
View at: Publisher Site | Google Scholar
M. Jokanović, “Biotransformation of organophosphorus compounds,” Toxicology, vol. 166, no. 3, pp. 139–160, 2001.
View at: Publisher Site | Google Scholar
M. R. Picciotto, M. J. Higley, and Y. S. Mineur, “Acetylcholine as a neuromodulator: cholinergic signaling shapes nervous system function and behavior,” Neuron, vol. 76, no. 1, pp. 116–129, 2012.
View at: Publisher Site | Google Scholar
L. L. Brunton, J. S. Lazo, and I. L. O. Buxton, Goodman & Gilman’s the Pharmacological Basis of Therapeutics, McGraw-Hill, New York, NY, USA, 12th edition, 2011.
A. C. Kruse, B. K. Kobilka, D. Gautam, P. M. Sexton, A. Christopoulos, and J. Wess, “Muscarinic acetylcholine receptors: novel opportunities for drug development,” Nature Reviews Drug Discovery, vol. 13, no. 7, pp. 549–560, 2014.
View at: Publisher Site | Google Scholar
J. A. Dani, “Neuronal nicotinic acetylcholine receptor structure and function and response to nicotine,” International Review of Neurobiology, vol. 124, pp. 3–19, 2015.
View at: Publisher Site | Google Scholar
R. C. Hogg, M. Raggenbass, and D. Bertrand, “Nicotinic acetylcholine receptors: from structure to brain function,” in Reviews of Physiology, Biochemistry and Pharmacology, pp. 1–46, Springer, Berlin, Germany, 2003.
View at: Google Scholar
M. Nakamura and I.-S. Jang, “Presynaptic nicotinic acetylcholine receptors enhance GABAergic synaptic transmission in rat periaqueductal gray neurons,” European Journal of Pharmacology, vol. 640, no. 1-3, pp. 178–184, 2010.
View at: Publisher Site | Google Scholar
N. Mine, W. Taniguchi, N. Nishio et al., “Synaptic modulation of excitatory synaptic transmission by nicotinic acetylcholine receptors in spinal ventral horn neurons,” Neuroscience, vol. 290, pp. 18–30, 2015.
View at: Publisher Site | Google Scholar
P. Manavalan, P. Taylor, and W. Curtis Johnson, “Circular dichroism studies of acetylcholine sterase conformation. Comparison of the 11 S and 5.6 S species and the differences induced by inhibitory ligands,” Biochimica et Biophysica Acta (BBA)—Protein Structure and Molecular Enzymology, vol. 829, no. 3, pp. 365–370, 1985.
View at: Publisher Site | Google Scholar
D. Nachmansohn and I. B. Wilson, “The enzymic hydrolysis and synthesis of acetylcholine,” Advances in Enzymology and Related Subjects of Biochemistry, vol. 12, pp. 259–339, 1951.
View at: Publisher Site | Google Scholar
P. Taylor and Z. Radic, “The cholinesterases: from genes to proteins,” Annual Review of Pharmacology and Toxicology, vol. 34, no. 1, pp. 281–320, 1994.
View at: Publisher Site | Google Scholar
G. Mooser and D. S. Sigman, “Ligand binding properties of acetylcholinesterase determined with fluorescent probes,” Biochemistry, vol. 13, no. 11, pp. 2299–2307, 1974.
View at: Publisher Site | Google Scholar
I. B. Wilson and C. Quan, “Acetylcholinesterase studies on molecular complementariness,” Archives of Biochemistry and Biophysics, vol. 73, no. 1, pp. 131–143, 1958.
View at: Publisher Site | Google Scholar
V. Tougu, “Acetylcholinesterase: mechanism of catalysis and inhibition,” Current Medicinal Chemistry—Central Nervous System Agents, vol. 1, no. 2, pp. 155–170, 2005.
View at: Google Scholar
P. Jayawardane, N. Senanayake, and A. Dawson, “Electrophysiological correlates of intermediate syndrome following acute organophosphate poisoning,” Clinical Toxicology, vol. 47, no. 3, pp. 193–205, 2009.
View at: Publisher Site | Google Scholar
L. Karalliedde, D. Baker, and T. C. Marrs, “Organophosphate-induced intermediate syndrome: aetiology and relationships with myopathy,” Toxicological Reviews, vol. 25, no. 1, pp. 1–14, 2006.
View at: Publisher Site | Google Scholar
E. J. Hulse, J. O. J. Davies, A. J. Simpson, A. M. Sciuto, and M. Eddleston, “Respiratory complications of organophosphorus nerve agent and insecticide poisoning. Implications for respiratory and critical care,” American Journal of Respiratory and Critical Care Medicine, vol. 190, no. 12, pp. 1342–1354, 2014.
View at: Publisher Site | Google Scholar
C. Curtil and P. Masson, “Aging of cholinesterase after inhibition by organophosphates,” Annales Pharmaceutiques Françaises, vol. 51, no. 2, pp. 63–77, 1993.
View at: Google Scholar
M. Wandhammer, E. Carletti, M. Van der Schans et al., “Structural study of the complex stereoselectivity of human butyrylcholinesterase for the neurotoxic V-agents,” Journal of Biological Chemistry, vol. 286, no. 19, pp. 16783–16789, 2011.
View at: Publisher Site | Google Scholar
K. Jeong and J. Choi, “Theoretical study on the toxicity of “Novichok” agent candidates,” Royal Society Open Science, vol. 6, no. 8, p. 190414, 2019.
View at: Publisher Site | Google Scholar
S. S. K. D. Gill and K. D. Gill, “Biochemical characterization of dichlorvos-induced delayed neurotoxicity in rat,” IUBMB Life (International Union of Biochemistry and Molecular Biology: Life), vol. 49, no. 2, pp. 125–130, 2000.
View at: Publisher Site | Google Scholar
N. Nand, H. K. Aggarwal, K. Bharti, and D. Chakrabarti, “Organophosphate induced delayed neuropathy,” JAPI, vol. 55, pp. 72-73, 2007.
View at: Google Scholar
D. R. Davies, Neurotoxicity of Organophosphorus Compounds, Springer, Berlin, Germany, 1963.
M. Lotti and A. Moretto, “Organophosphate-induced delayed polyneuropathy,” Toxicological Reviews, vol. 24, no. 1, pp. 37–49, 2005.
View at: Publisher Site | Google Scholar
A. Qureshi, R. Ali, M. Y. Yaqoob, and O. Saleem, “Organophosphate indduced delayed polyneuropathy,” Journal of the College of Physicians and Surgeons Pakistan, vol. 17, no. 7, pp. 441–443, 2007.
View at: Google Scholar
R. I. Krieger, Handbook of Pesticide Toxicology, Academic Press, Cambridge, MA, USA, 2001.
P. Glynn, “A mechanism for organophosphate-induced delayed neuropathy,” Toxicology Letters, vol. 162, no. 1, pp. 94–97, 2006.
View at: Publisher Site | Google Scholar
R. J. Richardson, N. D. Hein, S. J. Wijeyesakere, J. K. Fink, and G. F. Makhaeva, “Neuropathy target esterase (NTE): overview and future,” Chemico-Biological Interactions, vol. 203, no. 1, pp. 238–244, 2013.
View at: Publisher Site | Google Scholar
R. B. Hufnagel, G. Arno, N. D. Hein et al., “Neuropathy target esterase impairments cause Oliver-McFarlane and Laurence-Moon syndromes,” Journal of Medical Genetics, vol. 52, no. 2, pp. 85–94, 2015.
View at: Publisher Site | Google Scholar
J. S. Wentzell, M. Cassar, and D. Kretzschmar, “Organophosphate-induced changes in the PKA regulatory function of Swiss cheese/NTE lead to behavioral deficits and neurodegeneration,” PLoS One, vol. 9, no. 2, Article ID e87526, 2014.
View at: Publisher Site | Google Scholar
P. G. Richards, M. K. Johnson, and D. E. Ray, “Identification of acylpeptide hydrolase as a sensitive site for reaction with organophosphorus compounds and a potential target for cognitive enhancing drugs,” Molecular Pharmacology, vol. 58, no. 3, pp. 577–583, 2000.
View at: Publisher Site | Google Scholar
L. G. Costa and S. D. Murphy, “Cholinergic and opiate involvement in the antinociceptive effect of diisopropylfluorophosphate,” Pharmacology Biochemistry and Behavior, vol. 24, no. 3, pp. 733–736, 1986.
View at: Publisher Site | Google Scholar
R. W. Buntyn, N. Alugubelly, R. L. Hybart et al., “Inhibition of endocannabinoid-metabolizing enzymes in peripheral tissues following developmental chlorpyrifos exposure in rats,” International Journal of Toxicology, vol. 36, no. 5, p. 395, 2017.
View at: Publisher Site | Google Scholar
G. B. Quistad, S. E. Sparks, and J. E. Casida, “Fatty acid amide hydrolase inhibition by neurotoxic organophosphorus pesticides,” Toxicology and Applied Pharmacology, vol. 173, no. 1, pp. 48–55, 2001.
View at: Publisher Site | Google Scholar
G. B. Quistad, S. N. Liang, K. J. Fisher, D. K. Nomura, and J. E. Casida, “Each lipase has a unique sensitivity profile for organophosphorus inhibitors,” Toxicological Sciences, vol. 91, no. 1, pp. 166–172, 2006.
View at: Publisher Site | Google Scholar
P. Kovacic, “Mechanism of organophosphates (nerve gases and pesticides) and antidotes: electron transfer and oxidative stress,” Current Medicinal Chemistry, vol. 10, no. 24, pp. 2705–2709, 2003.
View at: Publisher Site | Google Scholar
G. Giordano, Z. Afsharinejad, M. Guizzetti, A. Vitalone, T. J. Kavanagh, and L. G. Costa, “Organophosphorus insecticides chlorpyrifos and diazinon and oxidative stress in neuronal cells in a genetic model of glutathione deficiency,” Toxicology and Applied Pharmacology, vol. 219, no. 2-3, pp. 181–189, 2007.
View at: Publisher Site | Google Scholar
B. P. Doctor and A. Saxena, “Bioscavengers for the protection of humans against organophosphate toxicity,” Chemico-Biological Interactions, vol. 157-158, pp. 167–171, 2005.
View at: Publisher Site | Google Scholar
E. H. Braue Jr. and S. T. Hobson, “Active topical skin protectants containing OPAA enzymes and clecs,” US Army, Washington, DC, USA, 2002, US Patent US6410604B1.
View at: Google Scholar
Y. J. Rosenberg, B. Laube, L. Mao et al., “Pulmonary delivery of an aerosolized recombinant human butyrylcholinesterase pretreatment protects against aerosolized paraoxon in macaques,” Chemico-Biological Interactions, vol. 203, no. 1, pp. 167–171, 2013.
View at: Publisher Site | Google Scholar
Y. J. Rosenberg, R. J. Adams, S. Hernandez-Abanto et al., “Pharmacokinetics and immunogenicity of a recombinant human butyrylcholinesterase bioscavenger in macaques following intravenous and pulmonary delivery,” Chemico-Biological Interactions, vol. 242, pp. 219–226, 2015.
View at: Publisher Site | Google Scholar
S. V. Lushchekina, L. M. Schopfer, and B. L. Grigorenko, “Optimization of cholinesterase-based catalytic bioscavengers against organophosphorus agents,” Frontiers in Pharmacology, vol. 9, p. 211, 2018.
View at: Publisher Site | Google Scholar
P. Masson and S. V. Lushchekina, “Emergence of catalytic bioscavengers against organophosphorus agents,” Chemico-Biological Interactions, vol. 259, pp. 319–326, 2016.
View at: Publisher Site | Google Scholar
F. M. Raushel and H. M. Holden, Phosphotriesterase: An Enzyme in Search of Its Natural Substrate, John Wiley & Sons, Hoboken, NJ, USA, 2006.
P.-C. Tsai, A. Bigley, Y. Li et al., “Stereoselective hydrolysis of organophosphate nerve agents by the bacterial phosphotriesterase,” Biochemistry, vol. 49, no. 37, pp. 7978–7987, 2010.
View at: Publisher Site | Google Scholar
A. N. Bigley and F. M. Raushel, “Catalytic mechanisms for phosphotriesterases,” Biochimica et Biophysica Acta (BBA)—Proteins and Proteomics, vol. 1834, no. 1, pp. 443–453, 2013.
View at: Publisher Site | Google Scholar
C. M. Daczkowski, S. D. Pegan, and S. P. Harvey, “Engineering the organophosphorus acid anhydrolase enzyme for increased catalytic efficiency and broadened stereospecificity on Russian VX,” Biochemistry, vol. 54, no. 41, pp. 6423–6433, 2015.
View at: Publisher Site | Google Scholar
P.-C. Tsai, N. Fox, A. N. Bigley, S. P. Harvey, D. P. Barondeau, and F. M. Raushel, “Enzymes for the homeland defense: optimizing phosphotriesterase for the hydrolysis of organophosphate nerve agents,” Biochemistry, vol. 51, no. 32, p. 6463, 2012.
View at: Publisher Site | Google Scholar
M. M. Meier, C. Rajendran, C. Malisi et al., “Molecular engineering of organophosphate hydrolysis activity from a weak promiscuous lactonase template,” Journal of the American Chemical Society, vol. 135, no. 31, pp. 11670–11677, 2013.
View at: Publisher Site | Google Scholar
G. Gotthard, J. Hiblot, D. Gonzalez, M. Elias, and E. Chabriere, “Structural and enzymatic characterization of the phosphotriesterase OPHC2 from Pseudomonas pseudoalcaligenes,” PLoS One, vol. 8, no. 11, Article ID e77995, 2013.
View at: Publisher Site | Google Scholar
D. F. Xiang, P. Kolb, A. A. Fedorov et al., “Functional annotation and three-dimensional structure of Dr0930 from Deinococcus radiodurans, a close relative of phosphotriesterase in the amidohydrolase superfamily,” Biochemistry, vol. 48, no. 10, pp. 2237–2247, 2009.
View at: Publisher Site | Google Scholar
Y. Zhang, J. An, W. Ye et al., “Enhancing the promiscuous phosphotriesterase activity of a thermostable lactonase (GkaP) for the efficient degradation of organophosphate pesticides,” Applied and Environmental Microbiology, vol. 78, no. 18, pp. 6647–6655, 2012.
View at: Publisher Site | Google Scholar
V. K. A. Bunescu and C. Sayer, “Characterization of a phosphotriesterase-like lactonase from the hyperthermoacidophilic crenarchaeon Vulcanisaeta moutnovskia,” Journal of Biotechnology, vol. 190, pp. 11–17, 2014.
View at: Google Scholar
C. Zhongli, L. Shunpeng, and F. Guoping, “Isolation of methyl parathion-degrading strain M6 and cloning of the methyl parathion hydrolase gene,” Applied and Environmental Microbiology, vol. 67, no. 10, pp. 4922–4925, 2001.
View at: Publisher Site | Google Scholar
Y.-J. Dong, M. Bartlam, L. Sun et al., “Crystal structure of methyl parathion hydrolase from Pseudomonas sp. WBC-3,” Journal of Molecular Biology, vol. 353, no. 3, pp. 655–663, 2005.
View at: Publisher Site | Google Scholar
J. Yang, C. Yang, H. Jiang, and C. Qiao, “Overexpression of methyl parathion hydrolase and its application in detoxification of organophosphates,” Biodegradation, vol. 19, no. 6, pp. 831–839, 2008.
View at: Publisher Site | Google Scholar
N. WU, D. Minjie, L. Guoyi et al., “Cloning and expression of ophc2, a new organphosphorus hydrolase gene,” Chinese Science Bulletin, vol. 49, no. 12, p. 1245, 2004.
View at: Publisher Site | Google Scholar
Y.-j. Shen, P. Lu, H. Mei et al., “Isolation of a methyl parathion-degrading strain Stenotrophomonas sp. SMSP-1 and cloning of the ophc2 gene,” Biodegradation, vol. 21, no. 5, pp. 785–792, 2010.
View at: Publisher Site | Google Scholar
X.-J. Yu, X.-D. Kong, J. Zhao et al., “Switching a newly discovered lactonase into an efficient and thermostable phosphotriesterase by simple double mutations His250Ile/Ile263Trp,” Biotechnology and Bioengineering, vol. 111, no. 10, pp. 1920–1930, 2014.
View at: Publisher Site | Google Scholar
J. Chen, Y. Zhao, H. Zhang, Z. Liu, and Z. Lu, “Improving methyl parathion hydrolase to enhance its chlorpyrifos-hydrolysing efficiency,” Letters in Applied Microbiology, vol. 58, no. 1, pp. 53–59, 2014.
View at: Publisher Site | Google Scholar
J. J. DeFrank and T. C. Cheng, “Purification and properties of an organophosphorus acid anhydrase from a halophilic bacterial isolate,” Journal of Bacteriology, vol. 173, no. 6, pp. 1938–1943, 1991.
View at: Google Scholar
M. C. J. Wilce, C. S. Bond, N. E. Dixon et al., “Structure and mechanism of a proline-specific aminopeptidase from Escherichia coli,” Proceedings of the National Academy of Sciences, vol. 95, no. 7, pp. 3472–3477, 1998.
View at: Publisher Site | Google Scholar
N. K. Vyas, A. Nickitenko, V. K. Rastogi, S. S. Shah, and F. A. Quiocho, “Structural insights into the dual activities of the nerve agent degrading organophosphate anhydrolase/prolidase,” Biochemistry, vol. 49, no. 3, pp. 547–559, 2010.
View at: Publisher Site | Google Scholar
C. M. Hill, W.-S. Li, T.-C. Cheng, J. J. DeFrank, and F. M. Raushel, “Stereochemical specificity of organophosphorus acid anhydrolase toward p-nitrophenyl analogs of soman and sarin,” Bioorganic Chemistry, vol. 29, no. 1, pp. 27–35, 2001.
View at: Publisher Site | Google Scholar
M. Melzer, J. C.-H. Chen, A. Heidenreich et al., “Reversed enantioselectivity of diisopropyl fluorophosphatase against organophosphorus nerve agents by rational design,” Journal of the American Chemical Society, vol. 131, no. 47, pp. 17226–17232, 2009.
View at: Publisher Site | Google Scholar
A. M. Latifi, A. Karami, and S. Khodi, “Efficient surface display of diisopropylfluorophosphatase (DFPase) in E. coli for biodegradation of toxic organophosphorus compounds (DFP and cp),” Applied Biochemistry and Biotechnology, vol. 177, no. 3, pp. 624–636, 2015.
View at: Publisher Site | Google Scholar
M. Elias, D. Liebschner, and J. Koepke, “Hydrogen atoms in protein structures: high-resolution X-ray diffraction structure of the DFPase,” BMC Research Notes, vol. 6, no. 308, pp. 1–7, 2013.
View at: Publisher Site | Google Scholar
M.-M. Blum and J. C.-H. Chen, “Structural characterization of the catalytic calcium-binding site in diisopropyl fluorophosphatase (DFPase)-comparison with related β-propeller enzymes,” Chemico-Biological Interactions, vol. 187, no. 1–3, pp. 373–379, 2010.
View at: Publisher Site | Google Scholar
T. Wymore, M. J. Field, P. Langan, J. C. Smith, and J. M. Parks, “Hydrolysis of DFP and the nerve agent (S)-sarin by DFPase proceeds along two different reaction pathways: implications for engineering bioscavengers,” The Journal of Physical Chemistry B, vol. 118, no. 17, pp. 4479–4489, 2014.
View at: Publisher Site | Google Scholar
D. Han, S. Filocamo, R. Kirby, and A. J. Steckl, “Deactivating chemical agents using enzyme-coated nanofibers formed by electrospinning,” ACS Applied Materials & Interfaces, vol. 3, no. 12, pp. 4633–4639, 2011.
View at: Publisher Site | Google Scholar
K. Kowalska, E. Socha, and H. Milnerowicz, “Review: the role of paraoxonase in cardiovascular diseases,” Annals of Clinical and Laboratory Science, vol. 45, no. 2, pp. 226–233, 2015.
View at: Google Scholar
D. Rochu, E. Chabrière, and P. Masson, “Human paraoxonase: a promising approach for pre-treatment and therapy of organophosphorus poisoning,” Toxicology, vol. 233, no. 1–3, pp. 47–59, 2007.
View at: Publisher Site | Google Scholar
J. Zielaskowska and D. Oleszewska-Słonina, “The polymorphism of paraoxonase and its effects in physiological and pathological processes,” Advances in Clinical and Experimental Medicine, vol. 15, no. 6, pp. 1073–1078, 2006.
View at: Google Scholar
C. L. Kuo and B. N. La Du, “Calcium binding by human and rabbit serum paraoxonases. Structural stability and enzymatic activity,” Drug Metabolism and Disposition: The Biological Fate of Chemicals, vol. 26, no. 7, pp. 653–660, 1998.
View at: Google Scholar
P. Masson, D. Josse, O. Lockridge et al., “Enzymes hydrolyzing organophosphates as potential catalytic scavengers against organophosphate poisoning,” Journal of Physiology-Paris, vol. 92, no. 5-6, pp. 357–362, 1998.
View at: Publisher Site | Google Scholar
L. Viguié and D. S. Tawfik, “High affinity, stability, and lactonase activity of serum paraoxonase PON1 anchored on HDL with ApoA-I,” Biochemistry, vol. 44, no. 35, pp. 11843–11854, 2005.
View at: Publisher Site | Google Scholar
K. Sumegová, P. Blazícek, I. Waczulíková, I. Zitnanová, and Z. Duracková, “Activity of paraoxonase 1 (PON1) and its relationship to markers of lipoprotein oxidation in healthy Slovaks,” Acta Biochimica Polonica, vol. 53, no. 4, pp. 783–787, 2006.
View at: Publisher Site | Google Scholar
S. L. Primo-Parmo, R. C. Sorenson, J. Teiber, and B. N. L. Du, “The human serum paraoxonase/arylesterase gene (PON1) is one member of a multigene family,” Genomics, vol. 33, no. 3, pp. 498–507, 1996.
View at: Publisher Site | Google Scholar
L.-P. Précourt, D. Amre, M.-C. Denis et al., “The three-gene paraoxonase family: physiologic roles, actions and regulation,” Atherosclerosis, vol. 214, no. 1, pp. 20–36, 2011.
View at: Publisher Site | Google Scholar
C. J. Ng, D. J. Wadleigh, A. Gangopadhyay et al., “Paraoxonase-2 is a ubiquitously expressed protein with antioxidant properties and is capable of preventing cell-mediated oxidative modification of low density lipoprotein,” Journal of Biological Chemistry, vol. 276, no. 48, pp. 44444–44449, 2001.
View at: Publisher Site | Google Scholar
S. T. Reddy, D. J. Wadleigh, V. Grijalva et al., “Human paraoxonase-3 is an HDL-associated enzyme with biological activity similar to paraoxonase-1 protein but is not regulated by oxidized lipids,” Arteriosclerosis, Thrombosis, and Vascular Biology, vol. 21, no. 4, pp. 542–547, 2001.
View at: Publisher Site | Google Scholar
D. I. Draganov, J. F. Teiber, A. Speelman, Y. Osawa, R. Sunahara, and B. N. La Du, “Human paraoxonases (PON1, PON2, and PON3) are lactonases with overlapping and distinct substrate specificities,” Journal of Lipid Research, vol. 46, no. 6, p. 1239, 2005.
View at: Publisher Site | Google Scholar
N. Shunmoogam, P. Naidoo, and R. Chilton, “Paraoxonase (PON)-1: a brief overview on genetics, structure, polymorphisms and clinical relevance,” Vascular Health and Risk Management, vol. 14, pp. 137–143, 2018.
View at: Publisher Site | Google Scholar
M. Najafi, L. H. Gohari, and M. Firoozrai, “Paraoxonase 1 gene promoter polymorphisms are associated with the extent of stenosis in coronary arteries,” Thrombosis Research, vol. 123, no. 3, pp. 503–510, 2009.
View at: Publisher Site | Google Scholar
B. Agachan, H. Yilmaz, H. A. Ergen, Z. E. Karaali, and T. Isbir, “Paraoxonase (PON1) 55 and 192 polymorphism and its effects to oxidant-antioxidant system in Turkish patients with type 2 diabetes mellitus,” Physiological Research, vol. 54, no. 3, pp. 287–293, 2005.
View at: Google Scholar
S. A. Oliveira, A. P. Mansur, C. C. Ribeiro, J. A. F. Ramires, and J. M. Annichino-Bizzacchi, “PON1 M/L55 mutation protects high-risk patients against coronary artery disease,” International Journal of Cardiology, vol. 94, no. 1, pp. 73–77, 2004.
View at: Publisher Site | Google Scholar
T. Fujita, J.-L. Mandel, T. Shirasawa, O. Hino, T. Shirai, and N. Maruyama, “Isolation of cDNA clone encoding human homologue of senescence marker protein-30 (SMP30) and its location on the X chromosome,” Biochimica et Biophysica Acta (BBA)—Gene Structure and Expression, vol. 1263, no. 3, pp. 249–252, 1995.
View at: Publisher Site | Google Scholar
T. Mori, A. Ishigami, K. Seyama et al., “Senescence marker protein-30 knockout mouse as a novel murine model of senile lung,” Pathology International, vol. 54, no. 3, pp. 167–173, 2004.
View at: Publisher Site | Google Scholar
R. K. Dutta, F. Parween, and M. S. Hossain, “Comparative analysis of the metal-dependent structural and functional properties of mouse and human SMP30,” PLoS One, vol. 14, no. 6, Article ID e0218629, 2019.
View at: Publisher Site | Google Scholar
Y. Kondo, A. Ishigami, S. Kubo et al., “Senescence marker protein-30 is a unique enzyme that hydrolyzes diisopropyl phosphorofluoridate in the liver,” FEBS Letters, vol. 570, no. 1–3, pp. 57–62, 2004.
View at: Publisher Site | Google Scholar
T. Fujita, “Senescence marker protein-30 (SMP30): structure and biological function,” Biochemical and Biophysical Research Communications, vol. 254, no. 1, pp. 1–4, 1999.
View at: Google Scholar
H. Inoue, T. Fujita, T. Kitamura et al., “Senescence marker protein-30 (SMP30) enhances the calcium efflux from renal tubular epithelial cells,” Clinical and Experimental Nephrology, vol. 3, no. 4, pp. 261–267, 1999.
View at: Publisher Site | Google Scholar
N. Shimokawa and M. Yamaguchi, “Molecular cloning and sequencing of the cDNA coding for a calcium-binding protein regucalcin from rat liver,” FEBS Letters, vol. 327, no. 3, pp. 251–255, 1993.
View at: Publisher Site | Google Scholar
S. Chakraborti and B. J. Bahnson, “Crystal structure of human senescence marker protein 30: insights linking structural, enzymatic, and physiological functions,,” Biochemistry, vol. 49, no. 16, pp. 3436–3444, 2010.
View at: Publisher Site | Google Scholar
M. S. Choi, A. Saxena, and N. Chilukuri, “A strategy for the production of soluble human senescence marker protein-30 in Escherichia coli,” Biochemical and Biophysical Research Communications, vol. 393, no. 3, pp. 509–513, 2010.
View at: Publisher Site | Google Scholar
E. S. Cedergren-Zeppezauer, G. Larsson, P. Olof Nyman, Z. Dauter, and K. S. Wilson, “Crystal structure of a dUTPase,” Nature, vol. 355, no. 6362, pp. 740–743, 1992.
View at: Publisher Site | Google Scholar
J. M. Harris, E. M. McIntosh, and G. E. O. Muscat, “Structure/function analysis of a dUTPase: catalytic mechanism of a potential chemotherapeutic target,” Journal of Molecular Biology, vol. 288, no. 2, pp. 275–287, 1999.
View at: Publisher Site | Google Scholar
K. Nyíri, H. D. T. Mertens, and B. Tihanyi, “Structural model of human dUTPase in complex with a novel proteinaceous inhibitor,” Scientific Reports, vol. 8, p. 4326, 2018.
View at: Publisher Site | Google Scholar
A. A. de Castro, F. V. Soares, A. F. Pereira et al., “Asymmetric biodegradation of the nerve agents Sarin and VX by human dUTPase: chemometrics, molecular docking and hybrid QM/MM calculations,” Journal of Biomolecular Structure and Dynamics, vol. 37, no. 8, pp. 2154–2164, 2019.
View at: Publisher Site | Google Scholar
M. Ben-David, G. Wieczorek, M. Elias, I. Silman, J. L. Sussman, and D. S. Tawfik, “Catalytic metal ion rearrangements underline promiscuity and evolvability of a metalloenzyme,” Journal of Molecular Biology, vol. 425, no. 6, pp. 1028–1038, 2013.
View at: Publisher Site | Google Scholar
Y. Ashani, R. D. Gupta, M. Goldsmith et al., “Stereo-specific synthesis of analogs of nerve agents and their utilization for selection and characterization of paraoxonase (PON1) catalytic scavengers,” Chemico-Biological Interactions, vol. 187, no. 1–3, pp. 362–369, 2010.
View at: Publisher Site | Google Scholar
G. Amitai, R. D. Gupta, and D. S. Tawfik, “Latent evolutionary potentials under the neutral mutational drift of an enzyme,” HFSP Journal, vol. 1, no. 1, pp. 67–78, 2007.
View at: Publisher Site | Google Scholar
R. D. Gupta, M. Goldsmith, Y. Ashani et al., “Directed evolution of hydrolases for prevention of G-type nerve agent intoxication,” Nature Chemical Biology, vol. 7, no. 2, pp. 120–125, 2011.
View at: Publisher Site | Google Scholar
A. N. Bigley, M. F. Mabanglo, S. P. Harvey, and F. M. Raushel, “Variants of phosphotriesterase for the enhanced detoxification of the chemical warfare agent VR,” Biochemistry, vol. 54, no. 35, pp. 5502–5512, 2015.
View at: Publisher Site | Google Scholar
C. M. Hill, W.-S. Li, J. B. Thoden, H. M. Holden, and F. M. Raushel, “Enhanced degradation of chemical warfare agents through molecular engineering of the phosphotriesterase active site,” Journal of the American Chemical Society, vol. 125, no. 30, pp. 8990-8991, 2003.
View at: Publisher Site | Google Scholar
E. I. Scharff, J. Koepke, G. Fritzsch, C. Lücke, and H. Rüterjans, “Crystal structure of diisopropylfluorophosphatase from Loligo vulgaris,” Structure, vol. 9, no. 6, pp. 493–502, 2001.
View at: Publisher Site | Google Scholar
V. Katsemi, C. Lücke, J. Koepke et al., “Mutational and structural studies of the diisopropylfluorophosphatase from Loligo vulgaris shed new light on the catalytic mechanism of the enzyme,” Biochemistry, vol. 44, no. 25, pp. 9022–9033, 2005.
View at: Publisher Site | Google Scholar
T. E. Reeves, M. E. Wales, J. K. Grimsley, P. Li, D. M. Cerasoli, and J. R. Wild, “Balancing the stability and the catalytic specificities of OP hydrolases with enhanced V-agent activities,” Protein Engineering Design and Selection, vol. 21, no. 6, pp. 405–412, 2008.
View at: Publisher Site | Google Scholar
J. K. Grimsley, B. Calamini, J. R. Wild, and A. D. Mesecar, “Structural and mutational studies of organophosphorus hydrolase reveal a cryptic and functional allosteric-binding site,” Archives of Biochemistry and Biophysics, vol. 442, no. 2, pp. 169–179, 2005.
View at: Publisher Site | Google Scholar
C. Mee-Hie Cho, A. Mulchandani, and W. Chen, “Functional analysis of organophosphorus hydrolase variants with high degradation activity towards organophosphate pesticides,” Protein Engineering, Design and Selection, vol. 19, no. 3, pp. 99–105, 2006.
View at: Publisher Site | Google Scholar
Y.-S. Jeong, J. M. Choi, H.-H. Kyeong, J.-Y. Choi, E.-J. Kim, and H.-S. Kim, “Rational design of organophosphorus hydrolase with high catalytic efficiency for detoxifying a V-type nerve agent,” Biochemical and Biophysical Research Communications, vol. 449, no. 3, pp. 263–267, 2014.
View at: Publisher Site | Google Scholar
C. M. Theriot, R. L. Semcer, S. S. Shah, and A. M. Grunden, “Improving the catalytic activity of hyperthermophilic Pyrococcus horikoshii prolidase for detoxification of organophosphorus nerve agents over a broad range of temperatures,” Archaea, vol. 2011, Article ID 565127, 9 pages, 2011.
View at: Publisher Site | Google Scholar
S. Y. Bae, J. M. Myslinski, L. R. McMahon et al., “An OPAA enzyme mutant with increased catalytic efficiency on the nerve agents sarin, soman, and GP,” Enzyme and Microbial Technology, vol. 112, pp. 65–71, 2018.
View at: Publisher Site | Google Scholar
A. Adamu, A. Aliyu, F. Huyop, and R. A. Wahab, “Molecular basis and engineering of enzymes stereospecificity,” Journal of Molecular Biology and Methods, vol. 1, no. 1, pp. 1–7, 2018.
View at: Google Scholar
G. Li, J.-b. Wang, and M. T. Reetz, “Biocatalysts for the pharmaceutical industry created by structure-guided directed evolution of stereoselective enzymes,” Bioorganic & Medicinal Chemistry, vol. 26, no. 7, pp. 1241–1251, 2018.
View at: Publisher Site | Google Scholar
M. T. Reetz, “Directed evolution of artificial metalloenzymes: a universal means to tune the selectivity of transition metal catalysts?” Accounts of Chemical Research, vol. 52, no. 2, pp. 336–344, 2019.
View at: Publisher Site | Google Scholar
G. Amitai, R. Adani, G. Yacov et al., “Asymmetric fluorogenic organophosphates for the development of active organophosphate hydrolases with reversed stereoselectivity,” Toxicology, vol. 233, no. 1–3, pp. 187–198, 2007.
View at: Publisher Site | Google Scholar
G. Amitai, L. Gaidukov, R. Adani et al., “Enhanced stereoselective hydrolysis of toxic organophosphates by directly evolved variants of mammalian serum paraoxonase,” FEBS Journal, vol. 273, no. 9, pp. 1906–1919, 2006.
View at: Publisher Site | Google Scholar
I. Cherny, P. Greisen, Y. Ashani et al., “Engineering V-type nerve agents detoxifying enzymes using computationally focused libraries,” ACS Chemical Biology, vol. 8, no. 11, pp. 2394–2403, 2013.
View at: Publisher Site | Google Scholar

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Copyright © 2020 Sudisha Mukherjee and Rinkoo Devi Gupta. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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